The present invention relates to a mass sensor for determining a minute mass of a nanogram (10xe2x88x929 g) order, for example, a mass sensor for sensing microorganisms such as bacteria, viruses, and protozoa (immune sensor), and a mass sensor for sensing moisture, toxic substances, or specific chemical substances such as taste components (moisture meter, gas sensor, and taste sensor), and a method for sensing a mass. In particular, the present invention relates to a mass sensor conveniently used for determining the mass of a substance to be sensed by measuring change in resonant frequencies caused by change in the mass of a diaphragm on which a catching substance for catching a substance to be sensed by reacting only with the object to be sensed is applied, and a method for sensing a mass.
Since the mass sensor of the present invention is not limited to the measurement of change in the mass of the catching substance applied on a diaphragm as described above, that is, not limited to the indirect measurement of change in the mass of a diaphragm, but it is naturally possible to sense change in resonant frequency due to change in the mass of the diaphragm itself, the mass sensor can also be used as a thickness meter for vapor-deposited films or a dew indicator.
Furthermore, even if the mass of the diaphragm is not changed directly or indirectly, the mass sensor of the present invention can also be used as a vacuum gauge, a viscosity meter, or a temperature sensor by placing it in an environment to cause a change in the resonant frequency thereof, that is, by placing it in a medium environment of gases or liquids having different degrees of vacuum, viscosity, or temperature.
Thus, although the mass sensor of the present invention can be used in various applications depending on its embodiments, the same basic principle is also applied to the measurement of change in resonant frequencies of the diaphragm and the resonating portion including the diaphragm.
Recent progress of scientific and medical technologies, and newly developed pharmaceuticals such as antibiotics and chemotherapy drugs have enabled the treatment of various diseases heretofore considered to be difficult to treat. Among what are referred to as diseases, microorganism examinations are essential for the treatment of diseases caused by microorganisms such as bacteria, viruses, or protozoa, to find their pathogens, to clarify their types, and to determine drugs to which they are sensitive.
At present, in the first stage of microorganism examinations, since the cause of a disease and the type of the pathogen can be estimated from the symptoms, various specimens, such as blood, are selected depending on the type of the disease, pathogens present in the specimens are morphologically identified, or antigens or the specific metabolites of pathogens (e.g., toxins or enzymes, etc.) existing in the specimens are immunochemically identified. These processes include smeartest, staining, or microscopy used in bacterioscopy, and in recent years, instantaneous identification has become possible by fluorescent antibody staining or enzymatic antibody staining.
Furthermore, the virus serological test, recently used in the detection of viruses, is a method for proving the presence of specific immunity antibodies that appear in the serum of a patient. Examples of the method include the complement fixation reaction in which the presence of antibodies or antigens is determined by adding complements to test blood, and by observing whether the complements react with antigens or antibodies in the blood and fix to the cell membranes of the antigens or antibodies, or destroy the cell membranes.
Except extremely special cases where symptoms have not been seen heretofore, and the disease is caused by a new pathogen which has not been discovered, in the treatment of diseases caused by microorganisms or the like, adequate treatment can be conducted by finding pathogens in an early stage through the microorganism test described above, and the patient can be led to recovery without worsening of the symptoms.
However, with methods such as smeartest, staining, and microscopy, the detection of microorganisms is often difficult depending on their quantities, and time-consuming treatment such as the culture of specimens on an agar is required at need. Also in the virus serological test, since measurements must be performed as a rule during both the acute stage and the convalescent stage for determination from the movement of the quantities of antibodies, there is the problem of time consuming from the point of view of prompt diagnosis.
As seen in the complement fixation reactions described above, when a substance to be sensed reacts with a catching substance which catches the substance to be sensed by reacting only with the specific substance to be sensed, microorganisms, the mass of the catching substance increases by the mass of the substance to be sensed, even slightly. Such an increase in the mass similarly occurs in the relationship between a catching substance (adsorbing substance) and a chemical substance such as a specific gaseous substance and a smell component, and also applies to the case where a substrate itself without change in the mass is a catching substance, on which a specific substance is deposited or added. On the contrary, when a reaction in which a substance to be sensed caught by a catching substance or the like is released occurs, the mass of the catching substance or the like slightly decreases.
As an example of a method for sensing change in such a small mass, U.S. Pat. No. 4,789,804 discloses, as shown in FIG. 28, a mass sensor 80 comprising a quartz oscillator 81 and electrodes 82, 83 facing the quartz oscillator. When any substance adheres externally on these electrodes 82, 83, the mass sensor 80 senses change in their mass using change in the resonant frequency of the thickness slip oscillation (shear mode oscillation) of the quartz oscillator 81 in the direction of the surface of the electrodes.
However, such a mass sensor 80 has a problem in that since the part on which an external substance adheres and the part for detecting resonant frequency are in the same location, for example, the resonant frequency is unstable when the piezoelectric properties of the mass sensor 80 itself vary due to the temperature of the specimen or change in temperature. Also, if the specimen is a conductive solution, and when the mass sensor 80 is immersed unprotected in the specimen, short-circuit between electrodes may occur. Therefore, the mass sensor 80 must be subjected to insulation such as resin coating.
In order to solve problems in such a mass sensor 80, the present inventors have disclosed in Japanese Patent Application No. 9-361368 various mass sensors for measuring change in resonant frequencies before and after the mass has been changed when a diaphragm is allowed to oscillate by directly or indirectly changing the mass of the diaphragm. An example is shown in FIG. 27. A mass sensor 30 has a construction in which a resonating portion, composed by joining a connecting plate 33 to a diaphragm 31, and joining a sensing plate 32 having a piezoelectric element 35 arranged on the surface to the connecting plate 33, is joined to the side of a sensor substrate 34 having rectangular sides. In this mass sensor 30, change in the mass thereof can be known easily in a short time by measuring change in the resonant frequencies of the resonating portion mainly due to change in the mass of the diaphragm 31.
However, such a mass sensor 30 has a problem of difference in sensitivity depending on whether the location where the mass of the diaphragm 31 changed is, for example, the central portion or the end portion of the diaphragm 31, even the same amount of change, and improvement for minimizing the difference in sensitivity is demanded. Also, the sensitivity can be improved by making the diaphragm 31 oscillate more easily. In addition, if improvement of the sensitivity is pursued and moreover, the spread of the diaphragm 31 can be pursued, by making the diaphragm 31 oscillate more easily, measurement of mass on a more micro level will become possible.
This invention aims to solve the above problems of micro-mass sensors, and according to the present invention, there are provided first to sixth mass sensors structurally classified described below.
That is, according to the present invention, provided is a mass sensor as a first mass sensor, comprising:
a connecting plate having one or more slit(s) and/or opening portion(s) to be formed therein and/or having a thin-walled portion and a thick-walled portion to be formed therein;
a diaphragm joined with the connecting plate at respective side surfaces thereof;
a piezoelectric element;
a sensing plate with the piezoelectric element being provided at least at one part on at least one surface of the sensing plate, which has its side surface joined with the counterpart of the connecting plate in the direction perpendicular to the joining direction of the diaphragm and the connecting plate; and
a sensor substrate with which at least a part of side surfaces of the connecting plate as well as the sensing plate are joined,
wherein the diaphragm, the connecting plate, the sensing plate, and the piezoelectric element form a resonating portion.
In addition, according to the present invention, provided is a mass sensor as a second mass sensor, comprising:
a connecting plate having one or more slit(s) and/or opening portion(s) to be formed therein and/or having a thin-walled portion and a thick-walled portion to be formed therein;
a diaphragm joined with the connecting plate at respective side surfaces thereof;
a piezoelectric element;
two sensing plates with the piezoelectric element being provided at least at one part on at least one surface of at least one of the sensing plates, which has its side surface joined with the counterpart of the connecting plate, and so as to sandwich the connecting plate, in the direction perpendicular to the joining direction of the diaphragm and the connecting plate; and
a sensor substrate with a part of which at least a part of side surfaces of the connecting plate as well as the sensing plate are joined,
wherein the diaphragm, the connecting plate, the sensing plate, and the piezoelectric element form a resonating portion.
And in this second mass sensor, in the case where the piezoelectric element has been provided only on one sensing plate, it is preferable that at least one slit in formed in the other sensing plate in which no piezoelectric elements are provided in the direction perpendicular to the joining direction of the sensing plate and the connecting plate. Also, from the point of view of improvement on measuring sensitivities, in case of arranging two piezoelectric elements respectively to be provided on the surfaces of the two sensing plates facing the same direction, it is preferable to make the direction of polarization of the piezoelectric film of each piezoelectric element opposite to each other.
Moreover, according to the present invention, provided is a mass sensor as a third mass sensor, comprising:
two connecting plates having one or more slit(s) and/or opening portion(s) to be formed therein and/or having a thin-walled portion and a thick-walled portion to be formed therein;
a sensor substrate;
a diaphragm joined with the connecting plates at respective side surfaces thereof, and being sandwiched, which assembly is bridged across a gap between the side surfaces of the recessed portion provided in the sensor substrate;
a piezoelectric element; and
a sensing plate with the piezoelectric element being provided at least at one part on at least one surface of the sensing plate, which is bridged across the gap between its lower side surface of the recessed portion and the side surface of the connecting plate in the direction perpendicular to the joining direction of the connecting plate and the diaphragm,
wherein the diaphragm, the connecting plate, the sensing plate, and the piezoelectric element form a resonating portion.
Here, a recessed portion means a portion consisting of side surfaces facing to each other and a bottom surface connecting these side surfaces. In the present invention, the bottom surface is not necessarily a plane, but may be changed to various shapes, such as providing a cavity or providing a protrusion, unless the measurement of the oscillation or resonant frequencies of the diaphragm is affected.
Next, according to the present invention, provided is a mass sensor as a fourth mass sensor, comprising:
two connecting plates having one or more slit(s) and/or opening portion(s) to be formed therein and/or having a thin-walled portion and a thick-walled portion to be formed therein;
a sensor substrate;
a diaphragm joined with the connecting plates at respective side surfaces thereof, and being sandwiched, which assembly is bridged across a gap between the bottom side surfaces of the recessed portion provided in the sensor substrate so as to face each other;
a piezoelectric element; and
four sensing plates with a piezoelectric element being provided at at least one part on at least one surface of two of said sensing plates which face each other with one of said connecting plate between, which is bridged across the gap between its side surface of the recessed portion and the side surface of the connecting plate in the direction perpendicular to the joining direction of said connecting plate and said diaphragm, and
a piezoelectric element positioned at least one part on at least one surface of at least one of said sensing plates facing to said connecting plate,
wherein said diaphragm, said connecting plate, said sensing plate, and said piezoelectric element form a resonating portion.
And in this fourth mass sensor, in the case where there exists any sensing plate to which the piezoelectric element is not provided, it is preferable that at least one slit is formed in the sensing plate in the direction perpendicular to the joining direction of the sensing plate and the connecting plate. On the other hand, in the case where two piezoelectric elements respectively are provided on the surfaces of the two sensing plates facing each other via the connecting plate, it is preferable to make the direction of polarization of the piezoelectric film of each piezoelectric element opposite to each other.
In addition, according to the present invention, provided is a mass sensor as a fifth mass sensor, comprising:
a first connecting plate and a second connecting plate having one or more slit(s) and/or opening portion(s) to be formed therein and/or having a thin-walled portion and a thick-walled portion to be formed therein;
a first diaphragm joined with said first connecting plate at respective side surfaces thereof, and a second diaphragm joined with said second connecting plate at respective side surfaces thereof, between which connecting plates a first sensing plate to which a piezoelectric element is provided at least on a part of at least one surface is bridged; and
a senser substrate joined with the first connecting plate and the second connecting plate on the side surfaces each other so that the sensor substrate is positioned on the side opposite to the first diaphragm and the second diaphragm,
wherein said diaphragm, said connecting plate, said sensing plate, and said piezoelectric element form a resonating portion.
In this fifth mass sensor, it is also preferable that respective side surfaces are joined so that the first connecting plate is sandwiched by the second sensing plate and the first sensing plate, and/or respective side surfaces are joined so that the second connecting plate is sandwiched by the third sensing plate and the first sensing plate, and the second sensing plate and the third sensing plate are joined so that the both of sensing plate is joined with the sensor substrate in the joining direction at least with the connecting plate. That is, the portions which are completed by joining respective sensing plates and respective connecting plates are fitted with the recessed portion provided in the sensor substrate, is preferable. It is preferable that the piezoelectric element is provided on at least one part of at least one surface of a second sensing plate and/or third sensing plate, or one or more slits are formed in the direction perpendicularly to the joining direction of a first sensing plate and a first connecting plate in a second sensing plate and/or a third sensing plate. In addition in the case where piezoelectric elements are provided on the second sensing plate and the third sensing plate, it is preferable to make the direction of polarization of the piezoelectric film of these piezoelectric elements and that of the piezoelectric film of the piezoelectric element provided on the first sensing plate opposite to each other.
Next, according to the present invention, provided is a mass sensor as a sixth mass sensor, comprising:
a first connecting plate and a second connecting plate having one or more slit(s) and/or opening portion(s) to be formed therein and/or having a thin-walled portion and a thick-walled portion to be formed therein;
a sensor substrate;
a piezoelectric element;
a sensing plate; and
a first diaphragm joined with the first connecting plate at respective side surfaces thereof, and a second diaphragm joined with the second connecting plate at respective side surfaces thereof, between which connecting plates a first sensing plate is bridged across the gap,
wherein the second sensing plate and the first sensing plate are joined with the first connecting plate so as to sandwich the first connecting plate at their side surfaces, and side surfaces of the third sensing plate, the first sensing plate, and the second connecting plate are joined to each other so that the second connecting plate is sandwiched by the third sensing plate and the first sensing plate, and the piezoelectric element is provided at least on a part of at least one surface of the second sensing plate and the third sensing plate respectively, and bottom side surfaces of the recessed portion provided in the sensor substrate are joined with the side surfaces of the first connecting plate and the second connecting plate, that the side surfaces are opposed to the joint side surfaces of the first diaphragm and the first connecting plate, and the second diaphragm and the second connecting plate, and the second sensing plate and the third sensing plate join with at least the side surface of the recessed portion.
And in this sixth mass sensor, it is also preferable that at least one slit is formed in the first sensing plate in the direction perpendicular to the bridging direction of the first sensing plate.
Now, in all of the first through sixth mass sensors of the present invention described above, the connecting plate is preferably formed by joining one thin plate and another plate- or post-like spring plate with one or more slit(s) and/or opening portion(s) together, and it is preferable to form a diaphragm, a connecting plate, a sensing plate, and a sensor substrate integrally. And the connecting plate itself is also preferably formed integrally.
In addition, in order to obtain such an integral structure, a method is used in which a thin plate forming a connecting plate, a diaphragm, and a sensing plate are integrally formed from a vibrating plate, and another plate- or post-like spring plate forming a connecting plate, are integrally formed from an intermediate plate, and the connecting plate is integrally formed by laminating the intermediate plate and the vibrating plate, and when the sensor substrate is formed by laminating the vibrating plate, the intermediate plate, and the base plate, the mass sensor of the present invention can be easily obtained in an integral structure.
Moreover, the thickness of the thin-walled portion of the connecting plate is preferably made thicker than the thickness of the diaphragm and/or sensing plate, and, in particular, when the thickness of the thin-walled portion of the connecting plate is made thicker than the thickness to be attained by adding the thickness of the sensing plate and of the piezoelectric element, the sensitivity can be planned to be improved, which is more preferable. Incidentally, it is also preferable to form one or more recessed portion(s) or through hole(s) in any optional shape on the sensor substrate, and to form a resonating portion on each of the inner circumferential surfaces of the recessed portion(s) or through-hole(s).
All the mass sensors of the present invention can be used suitably for the measurement of change in a micro mass. As an aspect of the use, there is a method in which a catching substance reacting with and catching a substance to be sensed is applied on a diaphragm, the resonant frequencies of the resonating portion in this state where the substance to be sensed has not been caught by the catching substance, and in the state after the substance to be sensed has been caught by the catching substance, and the mass of the substance to be sensed having been caught is measured from change in the measured resonant frequencies. In the method for using such a mass sensor, when the mass sensor has a plurality of diaphragms, the catching substance is not applied to at least one diaphragm, which can be used for referencing or the like. Also, by applying different types of catching substances to each of at least a plurality of diaphragms, different types of substances to be sensed can be sensed simultaneously.
In the mass sensor of the present invention, without depending on the above-described aspect, it is preferable that the resonating portions are provided at least at two or more places on the sensor substrate so as to increase the dynamic range by integrating signals derived from the respective resonating portions. Also, it is preferable to arrange two piezoelectric elements respectively to be provided on the surfaces of the two sensing plates facing the same direction, and to make the direction of polarization of the piezoelectric film of each piezoelectric element opposite to each other. Moreover, it is possible to divide at least one of piezoelectric elements into two, and use one for driving and the other for sensing, which will contribute to the improvement of measuring sensitivity. Moreover, it is possible to provide two piezoelectric elements at one resonating portion, and to use one piezoelectric element for driving and the other piezoelectric element for sensing, from which a similar effect is attainable. In addition, it is preferable to provide a piezoelectric element for sensing on a surface of the connecting plate.
Although the mass sensor of the present invention can be used in any environments, when it is immersed in a conductive solution on using, it is preferable to provide a position sensor consisting of a pair of electrodes on the middle position between the diaphragm and the piezoelectric element on the sensor substrate, so that the diaphragm is immersed in the solution but the piezoelectric element is not, so as to cause change in the mass mainly of the diaphragm, and to prevent the short-circuiting of the piezoelectric element. In addition, if the piezoelectric element, the electrodes of the piezoelectric element and electrode leads connected to the electrode are coated with a resin or glass insulation coating layer, it is convenient for the mass sensor to be used in a humid environment or in a liquid. At this time, fluorocarbon resin or silicone resin is preferably used as resin. Furthermore, it is preferable that a shield layer consisting of a conductive member is formed on at least a part of the surface of this insulation layer, so as to reduce noise and to improve measurement sensitivity.
In the mass sensor of the present invention, the sensor substrate, the diaphragm, the connecting plates, and the sensing plate are preferably fabricated using fully stabilized zirconia or partially stabilized zirconia. As the piezoelectric film of the piezoelectric element, a material consisting mainly of lead zirconate, lead titanate, or lead magnesium niobate is preferably used. The dimensional adjustment of at least any of the diaphragm, the connecting plates, and the sensing plate is preferably performed by trimming using laser processing or machining. Trimming using laser processing or machining is also preferably used for the dimensional adjustment of the electrodes of the piezoelectric element, thereby the available electrode area of the piezoelectric element can easily be adjusted.
Now, according to the present invention, provided is a mass sensing method comprising:
providing a mass sensor comprising:
a connecting plate having one or more slit(s) and/or opening portion(s) and/or having a thin-walled portion and a thick-walled portion formed in the connecting plate, a diaphragm joined with the connecting plate at respective side surfaces thereof, at least one sensing plate joined with the connecting plate at respective side surfaces thereof, and at least one piezoelectric element being provided so that at least one portion of the side surfaces of said connecting plate and said sensing plate are joined with a portion of side surfaces of the sensor substrate, and
measuring the resonant frequency with said piezoelectric element at least based either on xcexd mode swing oscillation or xcexdz mode swing oscillation, xcexd mode swing oscillation involving straight-line like reciprocal oscillation of said diaphragm with a perpendicular axis passing through perpendicularly at the center of the joint surfaces of said connecting plate and said sensor substrate being the center, in the direction in parallel with the surface of the said diaphragm and perpendicular with said perpendicular axis, and xcexdz mode swing oscillation involving swing-like reciprocal oscillation of said diaphragm with said perpendicular axis being center, in the direction in parallel with the surface of said diaphragm and perpendicular with said perpendicular axis, accompanied by movement in the direction perpendicular with the surface of said diaphragm.